1. Field of the Invention
Aspects of the present invention relate to a zoom lens optical system, and more particularly, to a zoom lens optical system having a hand-shaking correcting function.
2. Description of the Related Art
Generally, zoom lenses provided in still cameras or video cameras are required to be compact, while having superior optical performance, a large aperture, and a high zoom ratio. These zoom lenses are installed in such a way so that plural lens units simultaneously move for focal control along a predetermined axis. Of course, there are many different ways to design zoom lenses, and any number or type of lens units may be used.
A user captures images of an object while holding a still camera or a video camera, but hand-shaking inevitably occurs even though the user tries to keep the camera steady while taking the pictures. Recently, technology has been developed which enables a camera to automatically correct the hand shaking of its user. In particular, since cameras are becoming more compact and lightweight, the hand shaking problem is becoming more serious than ever. Furthermore, a camera user today frequently takes pictures while moving, and therefore has trouble keeping the camera steady. Thus, solving the problem of hand shaking has become an important consideration for attempting to achieve clear images.
A known principle of hand-shaking correction is to detect an amount of movement of a focused image caused by hand shaking, and then shift the image backwards by the detected movement amount, so that the image seems to stand still. Such hand-trembling corrections can be categorized into two categories: electronic hand-shaking correction, and optical hand-shaking correction.
Electronic hand-shaking correction is implemented in a charged-coupled device, or “CCD,” drive control mode, or implemented in a field memory vibration control mode. Optical hand-shaking correction is implemented in a mode using a variable vertical angle prism or in a mode using movement of some lenses.
However, electronic hand-shaking correction has the drawback of image degradation of 20-30% because not all the CCD pixels are used in the correction process. Therefore, it is preferable to use optical hand-shaking correction because it results in no image degradation.
FIG. 1 is a view for schematically showing a zoom lens optical system enabling optical hand-shaking correction. FIG. 1 shows a 3-CCD zoom lens optical system comprising a first lens unit 10, a second lens unit 20, a third lens unit 30, a fourth lens unit 40, an OLPF (Optical Low Pass Filter) 50, a prism assembly 60, and a CCD assembly 70.
The first lens unit 10 contains two convex lenses and one concave lens, and has positive (+) power in order for incident light to converge at a certain angle.
The second lens unit 20 is installed to move along an optical axis L to change a size of an image incident along the optical axis L of the first lens unit 10. The second lens unit 20 contains one convex lens and two concave lenses, and has positive (+) power.
The third lens unit 30 has one convex lens, transferring the image changed by the second lens unit 20 to the fourth lens unit 40.
The fourth lens unit 40 contains one convex lens and one concave lens and has positive (+) power, correcting the image passed through the third lens unit 30. The fourth lens unit 40 moves along the optical axis L, and performs image point movement corrections according to zooming operations and focusing operations based on changes in the distance between the fourth lens unit 40 and the object.
The OLPF 50 filters a wavelength of incident light in order for the wavelength to be below a certain bandwidth, so that light passed through the above lens units 10, 20, 30, and 40 and focused on the CCD assembly 70 does not form hot pixels.
The prism assembly 60 decomposes the filtered light by color, and transfers the decomposed color lights to the CCDs of the CCD assembly 70.
The CCD assembly 70 is formed in a 3-CCD mode having one CCD for each of the colors R, G, and B in order to enable the light decomposed by color through the prism assembly 60 to be focused as an image by color.
The third lens unit 30 moves up and down the optical axis L in order to correct the hand-shaking caused by a user. Specifically, if an image captured when the camera is still is focused at a position A and an image captured when the camera is shaken is focused at a position B, the third lens unit 30 moves itself in the direction perpendicular to the optical axis L to a distance substantially equal to the distance between the positions A and B in order for the focusing position to become the position A again.
However, if the third lens unit 30 is formed with only one lens as above, one problem is that that a big aberration variation occurs upon hand-shaking correction. Furthermore, there are limitations to the acquisition of high resolution when chromatic aberration correction and Optical Image Stabilizer (OIS) are applied.